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Maris Stella High School Name: ___________________

GCE O Level Biology Class (Index No.): Sec 3__ ( )2008 TYS Unit 2.1 Answers (Pure) Date: ________________

Unit 2.1 Answers (Nutrition inMammals)

Paper 2Question 1

(a) (i) Amylase;(ii) -q-q-q-q-q-q-q-q-q-q- ----------> q-q q-q q-q q-q q-q

Starch Amylase Maltose(iii) Buccal cavity; duodenum/ small intestine;

(b) (i) Emulsification due to action of bile salts;(ii) Hydrolysis/chemical digestion by lipases to fatty acids & glycerol;

Absorption of fatty acids & glycerol into epithelial cells of villus;

(c) Decrease in amount of fat absorbed, does not cause high levels of blood cholesterol/fat, henceless risk of coronary heart disease;No accumulation in the body, does not contribute to weight problems/obesity;

(d) Diet with all fats replaced with olestra would result in lack of fat in the body, which is animportant constituent of protoplasm (plasma membranes), and serves as insulating layer; (Fatswould be passed out in faeces, may lead to oily and loose stools.)

Question 2

Region E;

(b) (i) 2 hours ;(ii) Stomach;

(c) Drug K is in the dry form and would need to dissolve in water before it can be absorbed. It isenclosed in a few layers, preventing the drug from dissolving immediately upon contact withwater;Presence of an acid resistant coat, which does not break down in the stomach with the presenceof acid (drug still intact in stomach), and hence is not absorbed in the stomach;The drug would probably be absorbed in the small intestine/ileum, and hence the time taken forthe drug to reach its highest blood concentration would be longer compared to drug J;

(d) (i) The pill has a coat that tends to stick to mucus, which would cause it to be trapped inthe layer of mucus; hence taking a longer time before the drug enters the epithelialcells of the small intestine;

(ii) The partially permeable membrane allows the entry of water into the pill, which wouldcause the dry form of the drug to be dissolved;

After the drug is dissolved, it is able to move through the partially permeable membrane into

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the lumen of the small intestine;

Section B: Essay Questions1. (a) Describe what happens to fats as they pass through the following regions:

i) Mouth cavity (1m): No fat digestion; as no lipase is produced by the salivary glands;

ii)Duodenum (4m):

Bile from the liver emulsifies fat into smaller fat globules; increasing the surface area for action of lipase;Lipases from pancreas and intestinal glands; would hydrolyse/digest fat into fatty acids and glycerol;

iii)Rest of small intestine(5m):

In the ileum, Glycerol is soluble in water and it diffuses into the epithelium; Fatty acids are insoluble inwater. They form colloidal particles (soluble soaps) with bile salts which can easily dissolve in the

membrane of the epithelial cells and enter the cells; These fat particles are too big to diffuse into the blood

capillaries hence enter the lacteals (lymphatic capillaries); Glycerol also enters the lacteals; The glyceroland the fat particles mix with lymph to form a milky fluid called chyle and are carried away;

(b) What is the value of fat in the human body? (2m)

A source and store of energy that can be broken down to give large amounts of energy;

Stored under the skin as adipose tissue providing insulation, Solvent for fat-soluble vitamins, Used forsynthesis of cell membranes. (Any 1 for 1m)

2. (a) Describe the parts played in the digestion and assimilation of food by:

i) The pancreas

Secretes digestive enzymes (TAL) into the duodenum: Amylase hydrolyses starch into maltose, Trypsinhydrolyses proteins into peptides, Lipase hydrolyses fats into fatty acids and glycerol;;

Pancreatic juice is alkaline in nature hence neutralizes the acidic chyme and provides an optimal pH for

intestinal enzymes to function;*Secretes insulin into bloodstream which enables uptake and use of glucose by cells and controls

conversion of excess glucose into glycogen.

ii) The liverProduces bile which is stored in the gall bladder and released into the duodenum;

Bile emulsifies fats into fat globules to increase surface area for lipase action. Bile also enables absorption

of products of fat digestion;Liver oxidizes alcohol that is absorbed by the alimentary canal;

Excess amino acids are deaminated to form glucose and ammonia which is then converted to urea to be

excreted by the kidneys,;Excess glucose is stored in the liver as glycogen;

Fats are converted into other forms that can be easily oxidised or stored as adipose tissues;

[1/2m each]

2. (b) As a result of intestinal disease, parts of the alimentary canal are sometimes surgically removed.

Suggest the effect on lifestyle and on digestive function of removing:

i)The stomach:As the stomach secretes gastric enzymes such as rennin and pepsin, digestion of proteins is reduced;

The stomach churns the food, physically breaking them down to form chyme, hence the person can only

consume food that is easily digestible;The stomach is distensible and stores food temporarily. As the gut cannot accommodate large meals, the

person can only consume small portions of food;

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Hydrochloric acid is secreted in the stomach, hence bacteria will not be killed and the person becomes

more susceptible to bacterial infection;

ii) The colon:

The main function of the colon is the absorption of water and minerals;

Without the colon, diarrhoea may result, leading to loss of water and minerals; [1/2]

Person should replace water and mineral loss; [1/2]

3. Effects on Nervous System:Alcohol is a depressant. It slows down brain functions.

Self controlis reduced.Slurred speech, blurred vision, poor muscular co-ordination

Judgement deterioratesthus underestimation of speed occurs that can lead to automobile accidents.

High levels of alcohol (>0.7%) in the blood may paralyze the medulla oblongata or hind brain, which

controls breathing and heart beat and death occurs.

Effects on Digestive system:Acid secretion in stomach which increases the risk ofgastric ulcers.

Liver cirrhosis, a disease in which the liver cells are destroyed and replaced with fibrous tissue.Haemorrhage in the liver and liver failure can cause death as well.Alcoholics experience withdrawal symptomswhen they are deprived of alcohol. These include anxiety,

stomach upsets, sweating, goose pimples, watery of the eyes, vomiting, diarrhoea, convulsions andhallucinations. Deathmay occur in severe cases.

Effects on Society:

Alcoholics are liabilities to society.

They mayneglecttheir workandfamilies, and exhibit violentbehaviourespecially towards familymembers.Financial problemsare also incurred by alcoholics because of the amount spent on drinks or joblessness.

Many crimes have been committed by people under the influence of alcohol and many road accidents arecaused by drunk drivers.

Short term effects:Alcohol is a depressant. It slows down brain functions. It takes away a persons inhibitions and reduces

self control;

When intoxicated, a person may experienceslurred speech, blurred vision, poor muscular co-

ordination;

Poorjudgementandslower reactions. Underestimation of speed by drunk drivers often leads to

automobile accidents;

lHigh levels of alcohol (>0.5%) in the blood may paralyze the medulla oblongata or hind brain, whichcontrols breathing and heart beat and death occurs;

Long term effects:Increased acid secretion in stomach which increases the risk ofgastric ulcers;

Liver cirrhosis, a disease in which the liver cells are destroyed and replaced with fibrous tissue [1/2]

Haemorrhage in the liver and liver failurecan cause death as well. [1/2]

Prolonged drinking can lead to addiction such that alcoholics experience withdrawal symptomswhen theyare deprived of alcohol.[1/2]

These include anxiety, stomach upsets, sweating, goose pimples, watery of the eyes, vomiting, diarrhoea,convulsions and hallucinations. Death may occur in severe cases [1/2]